Modern system on chip (SoC) design strives to reduce manufacturing cost and power consumption. A smart power delivery network plays a role to reducing manufacturing cost and power consumption. A SoC circuit usually includes several subsystems of different device functionalities integrated on a single chip, which are powered at different voltage and current domains. To power those subsystems using a single power supply, for example, a battery of a smart phone, voltage regulators are needed. A voltage regulator converts a supply voltage to one or more target operation voltages.